Microwave generator



y 10,1951 R. s. BAILEY 2,559,582

' MICROWAVE cmmwon Filed April 10, 1948 2 swa 1 ll" .l .fl' N S INVENTOR. ROBE/P7 6'. 54/15) y 10, 1951 R. s. BAILEY 2,559,582

MICROWAVE GENERATOR Filed April 10, 1948 2 Sheets-Shane INVEN TOR. I F085)? T 61 MIL E Y A TTOFA EY oscillators of the Patented July 10, 1951 Robert S. Bailey,

New York, N. Y.,

orto

assign International Standard Electric Corporation,

New York, N. Y.,

a corporation of Delaware Application April 10, 1948, Serial No. 20,321

8 Claims. (Cl. 250-275) My invention relates to micro-wave generators and is particularly directed to improvements in magnetron type.

The conventional magnetron comprises a cathode and a coaxial anode or resonator structure containing a plurality of resonant cavities, a high potential direct current voltage source being connected between the cathode and anode structure. Magnet pole pieces are placed at the ends of the anode-cathode space to establish a steady magnetic field along the cathode and perpendicular to the electric field in said space, so that electrons starting from the cathode across the magnetic lines of force are given a component of velocity normal to both the electric and magnetic fields. When openings to the cavities are arranged along the resultant path of the electrons so that the electrons may successively traverse the openings, high frequency oscillations are excited in all the cavities; Such properties as electrons 'bunching, energy transfer between electrons and cavities, relations of transit times and cavity dimensions, and modes of operation, have been exhaustively treated in the prior art.

To increase the velocity of electrons which spiral about the cathode, for higher frequencies or greater power, the anode-cathode voltage and magnetic field intensities must be increased. Unfortunately, the small spacings and short insulating paths between the anode and cathode of the ating frequency and openings to the cavities arranged in a circle. The electron collecting electrode may be the anode or resonator block as in prior art devices. The electron collecting electrode may, alternatively, be positioned in the center of the space enclosed by the anode structure in the case of the cyclotron-magnetron. An electron source and associated electron accelerating means are placed'exteriorly of said space conventional magnetron places a definite limitation on the maximum voltage that may be employed' and hence limits the top speed of the electrons. This maximum voltage must bekept lower than is desired. For example, magnetrons of the rising sun type designed for 10 centimeter waves may have anode-cathode spacings of the order of 0.20 inch, magnetic flux densities of 1000 to 3000 gauss, and anode-cathode voltages of only 10 to 25 kilovolts. Even with such voltage gradients inside the envelope, dangerous leakage currents and actual arc-over easily occur. The slightest amount of gas in such gradients will ionize and initiate arcing, and cathode material condensed on protruding anode points will cause troublesome back-emission.

The object of my invention is an-improved micro-wave generator.

A more specific object of my invention is a micro-wave generator of the magnetron type which effectively obviates the limitations of high anode-cathode voltages.

The generator of my invention comprises, essentially, an anode or resonator structure with cavities designed for resonance at a desired opertion,

with means to direct high velocity electrons into said space. The effects of an intense electric field in said space is thus obtained without in fact having such a field in the space. A magnetic field is also established in the anode space of such direction and intensity as to spiral the injected electrons successively past the cavity openings at velocities heretofore unattained. That is, the injected electrons may be given velocities corresponding to electron voltages much higher than any static voltage that could be tolerated between electrodes of the conventional magnetron.

The scope of my invention is defined specifically in the appended claims and exemplary embodiments thereof are described in the following specification and shown in the accompanying drawing in which Fig. 1 is a longitudinal sectionwith the magnets omitted of one micro-wave generator of my invention, viewed on line l--l of Fig. 2,

Fig. 2 is a view of the section taken on line 2-2 of Fig. 1, with the magnets shown in posi- Fig. 3 is a longitudinal section with the magnets omitted of a second embodiment of my novel generator, viewed on line 3-3 of Fig. 4, and

Fig. 4 is a view of the section taken on line 4-4 of Fig. 3, with the magnetsgshown in position.

Accelerated electrons may, according to my invention, be projected into the electron interaction space of the resonator structure of any desired magnetron, the familiar cavity and slot resonator being shown in Fig. l. A solid bloclr I of metal such as copper is machined, fabricated with stampings, or cast with a plurality of cavities 2 and inwardly extending radial slots 3 of calculated dimensions for the desired frequency of operation. The inner ends of the metal segments 4 between the slots enclose anddefine a cylindrically symmetrical electron interaction space 5. The poles 6, shown in Fig. 2, of an electromagnet, or of a permanent magnet, at the ends of the interaction space establish steady magnetic flux lines generally parallel to the. axis of the space. According to known electromagnetic principles, electrons travelling with a finite velocity across flux lines are subject to a force normal to both the direction of the flux and the direction of;initial velocity, so that the resultant path of the electron is curved in a plane perpendicular to the flux. By proper adjustment of the magnitude of the magnetic field and of the electric field, initial electron velocity, here, the electrons may be made to travel in a circular path substantially concentric with the interaction space, so that energy may be transferred from the moving electrons to the high frequency electric iieids fringing the inner ends of the slots. The space phase and harmonic relations of the moving electrons with respect to the time phase of the fringing field at the slots determine the so-called mode of operation, the pi (1') mode being common.

According to an important feature of my invention, the usual cathode within the interaction space is eliminated, and the need for high anodecathode voltages within the magnetron envelope is removed. Instead, the desired electron voltage is imparted to electrons exteriorly of the magnetron by a particle accelerator and projected into the space. Preferably, the electrons enter the space more or less tangentially to the desired circular ath of electrons within the space. The line of approach of the injected electrons, however, may be within or entirely without this circular path. As soon as the electrons enter the field of infiuenceof trajectory, of course. begins to bend.

The particle accelerator shown is a Betatron, the toroidal envelope 1 of which contains an electron source 8. The source may be a directly or indirectly heated cathode 9. and may continuously emit or not into the magnetic field. That is, the cathode may be open to the envelope space or enclosed in a gun structure with an accelerating grid l and a control grid H for selectively suppressing emission. Magnet pole pieces 12 are coextensive with and disposed on both of the fiat sides of the envelope, the core l3 linking with the winding ll which is connected, in this embodiment, to a source of sinusoidal alternating current. By the known principles of the Betatron, the electrons are accelerated by the magnetic field while the magnitude of the magnet field changes and by proper adjustment of the operating parameters, the electrons are accelerated throughout the first V cycle of the sine voltage applied to the magnet so that these electrons may the magnetron magnet, their of accelerated electrons may be fed into the magnetron for a continuous radio frequency output as by applying a wave of sawtooth shape to the reach velocities corresponding to many millions H of volts if desired. As the velocity of these electrons increases their orbital radius increases in a predetermined manner and they may be made to leave the the gate I5 and along the guide tube IS. The guide tube is placed at the desired angle of entry into the interaction space in the magnetron. If envelopes separated as to vacuum are desired, an electron permeable window may be sealed gas outer periphery of the envelope through tight across one or both ends of the guide tube.

In operation, the high velocity electrons enter the magnetron and give up their kinetic energy to the micro-wave oscillations in the cavities of the resonator.

With a sine wave supplied to the Betatron magnet, pulses only of electrons flow through the guide tube to the magnetron so that the magnetron output comprises pulses of radio frequency waves of a pulse frequency equal to the fresaid sine wave. The magnetron output quency of pulses may be modulated as to amplitude, phase,

, 01' width by correspondingly modulating the elecsupplying a steady stream of high speed electrons to the magnetron.

Many resonator structures for magnetron oscillations can be conceived into which accelerated electrons may be projected for supplanting the usual cathode in the structure. In Figs. 8 and 4 is shown a magnetron of the cyclotron type. Two resonant cavities H on opposite sides of the resonator block communicate with the radial slots 18. Here, the interaction space I! in whichthe electrons may spiral is relatively large in diameter and sandwiched between parallel disc shaped halves of the resonator block. The normal circular trajectory of the electrons, in this resonator, carries the accelerated electrons across the side edges of the cavity slots as distinguished from the end edges as in Fig. 1. Discs 20 of glass, ceramic, or other insulating material are hermetically sealed to opposite sides of the resonator block, and theelectron collecting electrode 2| is .convefiiently insulated and supported centrally in the resonator by the discs.

The accelerator shown in Figs. 3 and 4 is also of the Betatron type, having a toroidal envelope 1, electron source 8, magnet 12, and a communicating guide tube l6, as in Figs. 1 and 2.

The advantages of removing the cathode from the electron interaction space are numerous. The usual barium strontium carbonates of the cathode need not be reduced and activated within the resonator, so that gas from this source is eliminated. Secondly, there is no cathode material present to evaporate and condense on the resonator structure and cause secondary and back emission. But, equally important is the elimination of the deleterious effects of high voltage gradients within the resonator. Lastly, 'there are no practical limits placed on the electron voltages that may be employed in anynovel generator, so that the frequency or the power of,

for accelerating electrons to high velocity, and' means defining a duct interconnecting said accelerator and said chamber to guide accelerated electrons from said accelerator into said interv action chamber in a plane substantially normal to said axis.

2. A resonator according to claim 1, wherein the duct between said accelerator and said interaction chamber is disposed substantially tangentially with respect to said interaction chamber.

8. A resonator according to claim 1, wherein -the accelerator comprises a body containing an annular chamber, a source of electrons in said chamber and the duct connecting the accelerator to said interaction chamber is disposed tangentially with respect to said annular chamber.

4. A resonator according to claim 3, further including two envelopes, one containing the body having the interaction chamber and the other containing the body having the annular chamber.

5. A resonator according to claim 3, further including an electron collector disposed centrally of said interaction chamber.

6. A generator comprising a resonator structure having a body containing an electron interaction chamber, a plurality of cavity resonators and ducts connecting the interaction chamber with each of said cavity resonators, an electron collecting electrode insulatively supported centrally in said interaction chamber, a source of high velocity electrons and means providing a duct interconnecting said source and said chamber to guide electrons moving at a high velocity from said source into said interaction chamber.

7. A generator according to claim 6, wherein the source of high velocity electrons includes a cathode, an annular chamber and means for producing lines of magnet flux cross-wise of said REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,232,050 Clavier et a1 Feb. 18, 1941 2,270,777 Von Baeyer Jan. 20, 1942 2,289,220 Smith July 7, 1942 2,409,038 Hansell Oct. 8, 1946 2,412,824 McArthur Dec. 17, 1946 2,423,716 McArthur July 8, 1947 2,437,279 Spencer Mar. 9, 1948 

